A specified number of balls taken as a unit. Balls in a lot are manufactured under presumed uniform conditions and should have very similar characteristics.

Grade

The guaranteed roundness of a ball identified in millionths of an inch. The grade designation is based on a combination of tolerances including dimension, surface roughness, and sphericity. The lower the grade value, the higher the precision of the ball.

Surface Roughness

A measure of the texture of the surface of the steel ball. It is quantified by a measure of the vertical deviations of a real surface from its ideal form. Irregularities on the surface of balls having height, width, and direction.

Sphericity (Deviation from Spherical Form)

A measure of how spherical or the roundness of the steel ball. This is measured by the radial distance from the maximum peak of a perfect circle to the maximum valley from the perfect circle.

T.I.R. (Total Indicated Runout)

A measure of the concentricity of a drilled ball usually measured by a dial indicator.

Nominal Ball Diameter

The value used to make a general identification of a ball size. Eg…1/8” ball.

Ball Diameter Variation

The difference between the largest and smallest actual single diameter measurement.

Lot Diameter Variation

The difference between the mean diameter of the largest ball and the mean diameter of the smallest ball in the lot.

Case Hardening

A heat treatment or a combination of heat treatments of surface hardening involving a change in the composition of the outer layer of an iron-base alloy in which the surface is made substantially harder by inward diffusion of a gas or liquid followed by appropriate thermal treatment. Typical hardening processes are carburizing, cyaniding, carbo-nitriding and nitriding.

Case Depth

The thickness of the case of a hardened steel ball.

Surface Hardness

The ball surface’s ability to withstand penetration by a specific indenting shape. Rockwell testing is one method of measuring surface hardness. It uses a dial reading which indicates the depth of penetration of a steel ball for softer steels and a diamond cone for heat treated and harder steels when a load is applied.

Core Hardness

The ball core’s ability to withstand penetration by a specific indenting shape. The core of the ball is the volume of the sphere below the case of the ball.

Microstructure

The structure of a prepared surface or thin foil of material as revealed by a microscope above 25× magnification. The microstructure of a material can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behavior, wear resistance, and so on, which in turn govern the application of these materials in industrial practice.

Surface Condition

The existence of cracks, pits and rust on the surface of balls when examined visually without magnification.